Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

FXUS61 KLWX 120857

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
357 AM EST Mon Feb 12 2018

A cold front will gradually move south of the area by late
today. High pressure will cross north of the area Tuesday. A
warm front will cross the region during midweek, followed by a
cold front late in the week.


As of 3 AM, the cold front was pushing southeast across east-
central Virginia and southern Maryland. However, observed
temperatures show that most guidance is pushing the cooler air
across the region a bit too quickly, so slowing down the push
resulted in a necessary nudge upward of highs for today... these
highs will likely be set early this morning with temps falling
for some time afterward. They may rebound a bit later this
after the clouds break for some sun, but not much.

Speaking of clouds...most if not all of the region remains
cloudy at this hour. This is due to the fact we remain in the
right entrance region of the strong jet streak located over the
northeastern US. In addition, we still have a shortwave moving
in from the west this morning and additional PVA moving up from
the south. This all combines with the cold front pushing south
of this region, resulting in an anafrontal configuration. Thus,
it now appears showers will continue developing along and
especially southeast of the US 29/I-95 corridor this morning,
especially the first portion. Rainfall will not be heavy given
the surface forcing is now to the southeast and PWs are
dropping, but the odds of a wet rush hour are pretty high,
especially in southern MD and east-central VA.

As the shortwave and jet streak finally slide east of the region
later today, the precip should end, clouds should break, and the
sun looks likely to reappear for the first time in several days.


Surface high pressure slides eastward across the Great Lakes
tonight and New England on Tuesday, with a wedge developing east
of the mountains. This will continue funneling Canadian air
into our region. Clear skies tonight under the high`s influence
will promote lows that are right around normal for mid
February, generally in the 20s. On Tuesday, things change, as
warm advection starts on the backside of the high, overtop the
wedge. The result will be increasing clouds, and this should
keep highs below normal, with many locales struggling to get out
of the 30s. Clouds will remain thick Tuesday night, but temps
may manage to fall back below freezing. However, at this point
forcing looks so weak that little to no precipitation will fall
during the night.

Warm advection grows strong Wednesday and Wednesday night as the
high slides further east off the coast and a warm front lifts
north across the region. A weak mid-level disturbance will also
cross the region, and a jet streak will also approach from the
west. All of these will combine to keep a decent amount of cloud
cover around on Wednesday, with a good chance of showers on
Wednesday night. Highs on Wednesday should be higher thanks to
the warm advection, with 50s looking common, but given chance of
clouds lingering, held them back from what some of the warmer
guidance is suggesting. Lows Wednesday night should stay above
freezing, with most places likely not dropping below the 40s.


There`s relative agreement in the overall pattern of the
extended forecast amongst model guidance. On Thursday, high
pressure will be off the southeast coast with WSW flow aloft
around an upper high in the Gulf of Mexico. Low pressure will be
developing in the mid Mississippi Valley, with moisture
advecting ahead of it. Chances of rain will increase as the day
progresses. Have not deviated from blended temperature guidance
at this point, but am concerned the forecast of 65-70 could be
ambitious if rain develops as indicated along with a weak wave
low passing across northern parts of the CWA. Baroclinic zone
will remain near the area through Friday, so rain chances will
remain on the high side. Surface low will lift to the northeast
on Friday, with height falls over the Great Lakes pushing the
front to the southeast. Showers will likely continue until the
front passes. Some periods of moderate rain will be possible
with this system as precipitable water values rise back over an
inch. Temperatures will be highly dependent on the timing of the
front, as decent cold advection will be found in its wake. In
the slowest timing, showers may linger into the evening across
southern parts of the area, but it does look like moisture
departs before cold air arrives. The one exception would be west
of the Allegheny Front, where a period of upslope snow showers
will be possible.

Model consensus has high pressure building across the area on
Saturday with temperatures near seasonal averages. At this time,
it looks like the high will stay in control through Sunday,
with temperatures moderating as surface flow turns southerly.


Generally VFR through the next several days. This morning, some
brief MVFR cigs are possible as showers cross the region, with
the greatest threat of showers being at CHO and DCA, with a
lesser chance at IAD/BWI/MTN and MRB most likely to stay dry and
VFR. Northwest wind may be gusty at times, but generally staying
below 30 knots. Winds diminish tonight and stay light on Tuesday
with VFR continuing. Will need to watch for potential of lowered
cigs Tuesday night through Wednesday night with warm moist air
moving back north, with the best shot of sub-VFR looking like
Wednesday night as showers move through. Wind should remain
light in this period.

Periods of sub-VFR conditions will be possible Thursday into
Friday as a low pressure system brings rain at times. A cold
front will cross Friday, ending the showers and bringing gusty
NW winds.


SCA for all waters through today as cold air pushes back into
the region behind a cold front. Wind should start to diminish
this afternoon and while parts may need a modest extension,
generally think its done by early evening. Sub-SCA winds should
predominate tonight through Wednesday night as high pressure
slides past us to the north.

Low pressure will pass northwest of the waters Thursday into
Thursday night. Southwesterly winds could reach SCA criteria on
portions of the waters, though overall mixing will be poor. A
cold front will cross the area on Friday, with northwesterly
winds potentially reach SCA criteria in its wake.


MARINE...Small Craft Advisory until 6 PM EST this evening for


MARINE...ADS/RCM is the U.S. government's official web portal to all federal, state and local government web resources and services.